1. Field of the Invention
This invention relates to a vehicle suspension system, and more specifically, to a suspension system of the type which has a variable suspension characteristic controlled in response to the traveling conditions of a vehicle.
2. Description of the Prior Art
There has been known a vehicle suspension system of the type referred to above in which, as shown for example in Japanese Unexamined Utility Model Publication No. 55(1980)-109008, the suspension characteristic of a suspension system is varied in response to the traveling speed of the vehicle so as to provide good maneuverability at all times. This serves to provide an intensified understeer characteristic during high speed traveling of the vehicle and a neutralsteer or a weak oversteer characteristic during low speed traveling so that there is always obtained highly stabilized maneuverability variable in response to changes in vehicle speed.
However, there are various factors other than the vehicle speed which require a change in maneuverability. For example, the magnitude of the steering angle has a close relation to the required maneuverability, and when the steering wheel is turned through a large angle, a weak understeer characteristic is desirable. In other words, it is desired that the understeer characteristic be weakened at a large angle of steering but be intensifies at a small angle of steering. Therefore, it is not possible to ensure satisfactory traveling stability only by controlling the maneuverability in accordance with the vehicle speed.
It is preferred that, for example, when the steering wheel is suddenly turned to greatly change the traveling direction of the vehicle, the understeer characteristic be weakened to approach the oversteer characteristic so that steering response is improved to make the steerable wheels sharply respond to the turning motion of the steering wheel. However, when the vehicle is being driven to run straight forward without any turning motion of the steering wheel, a strong understeer characteristic is preferred because this provides good straight-running capability. An understeer characteristic particularly facilitates correction of the heading or running attitude of the vehicle when it is affected by external disturbances, and if the understeer characteristic is decreased, the straight-running stability is reduced to make the vehicle dangerous during travel at high speed. Accordingly, it is desirable that the understeer characteristic be at all times changed to the optimal intensity with variation in the angle of steering.